No Disc Wheel for Ullrich

Why isn't T-Mobile and Ullrich riding a disc in the back? Is that four spoke up front and back more aerodynamic? I find that hard to believe. I remember earlier in the season he had a disc at soem TT, when he came back to racing in tour of germany I noticed he didn't have the disc back. Anyone heard anything? I thought he would be all over anything to give him an edge over, or at least equal, armstrong. Especially considering his considerable TT skills.

"Training is what Iím doing while my opponents are sleeping in."- Bill Robertson